BACKGROUND The most frequent i.v. iron preparations used for haemodialysis patients are iron dextran, iron gluconate and iron saccharate. Possible side effects include anaphylactic reactions due to preformed antibodies to dextran or vascular reactions due to unbound iron during treatment with iron gluconate or iron saccharate. METHODS Four dosage regimens of i.v. iron saccharate therapy were studied: 10, 20, 40 and 100 mg, which were given over a time period of 1 min after the end of the dialysis session. Iron metabolism parameters (serum iron concentrations, transferrin saturation and serum ferritin levels) were measured at 0, 1, 5, 15 and 30 min after application and immediately prior to the next dialysis session. All 18 regular haemodialysis patients studied received recombinant human erythropoietin (rHuEpo). RESULTS Serum iron levels and transferrin saturation increased significantly following i.v. injection of all doses of iron saccharate. Iron 'oversaturation' of transferrin iron binding did not occur in patients with transferrin levels > 180 mg/dl. However, in patients with transferrin levels < 180 mg/dl the injection of 100 mg iron saccharate resulted in a transferrin saturation of 102.6 +/- 39.5% (two patients with transferrin levels of 87 and 92 mg/dl had transferrin saturation of 119.8 and 149.7%, two patients with transferrin levels of 148 and 171 mg/dl had transferrin saturations of 77.9 and 63.1%, respectively). Serum ferritin levels remained unchanged during the post-injection period and increased by the next dialysis session following injection of 100 mg iron saccharate by 165%. CONCLUSIONS It is concluded that intravenous iron saccharate injection (10-100 mg even within 1 min) does not result in 'oversaturation' of transferrin iron binding if serum transferrin levels are > 180 mg/dl (high-risk patients; transferrin < 100 mg/dl). This may explain, at least in part, the minimal side effects observed during the i.v. application of iron saccharate. Low-dose i.v. iron saccharate (10-40 mg) is recommended for iron supplementation of haemodialysis patients. If injection of 100 mg is necessary, serum transferrin level should exceed 180 mg/dl. There is, however, no need for fast i.v. injection during routine iron supplementation.